System and method for identifying tissue using low-coherence interferometry

ABSTRACT

An apparatus for needle biopsy with real time tissue differentiation using one dimensional interferometric ranging imaging, comprising a biopsy device having a barrel and a needle, an optical fiber inserted in the needle, and a fiber optic imaging system connected to the optical fiber. The imaging system obtains images and compares the optical properties and patterns to a database of normalized tissue sample images to determine different tissue types. The physician performing the biopsy obtains feedback via a feedback unit associated with the biopsy device and which is connected to the imaging system. The feedback unit can provide visual, audible or vibratory feedback as to tissue type encountered when the needle is inserted toward the target tissue. The feedback unit can be programmed for different biopsy procedures so that the user can actuate a button to select a display or other feedback mechanism for the desired procedure and anticipated tissue to be encountered.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 60/442,392 filed Jan. 24, 2003, entitled “Devices and Methods forTissue Identification Using Low-Coherence Interferometry,” which isincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus and method for identifyingtissue types using interferometric ranging during needle biopsy. Moreparticularly, the present invention relates to an imaging systemincluding a needle probe and algorithms for detecting various tissuetypes during a biopsy. Also provided is a method for differentiatingtissue types using the imaging system.

2. Background of the Invention

A significant cause of inefficiency of intraoperative and biopsyprocedures is the inability of a physician to identify tissue type bygross inspection. For example, head and neck surgeries, the inability todifferentiate muscle, fat, lymph node, and parathyroid glands by grossinspection leads to unnecessary operative time, resulting in an increasein the cost of these procedures. Further, when not guided by an imagingmodality, fine needle aspiration biopsies yield non-diagnostic tissue in25% to 35% of cases. In medicine, there is a significant need for aninexpensive, portable, and efficient way for identifying tissue type.

The use of optical coherence tomography and confocal microscopy inneedle probes has been previously described. These needle probes allowphysicians to acquire images of tissue. However, these conventionalneedle probes have certain shortcomings. The methods used in theseneedle probes require imaging a single focused spot on a sample byscanning the spot in two dimensions in order to produce a twodimensional image of the subject. The scanning and imaging requirementsof these known imaging needle probe systems require complex andexpensive disposable components, as well as console components. Manycomponents of existing imaging needle probes require complex andexpensive construction making routine use of the needle probes apractical impossibility. Further, current imaging needle probes usecomplex and expensive custom syringes, which may not be sterilizable ordisposable.

In the past, research has been performed to evaluate the use oflow-coherence interferometry (“LCI”) imaging for tissue diagnosis.Optical coherence tomography (“OCT”) is LCI imaging that is performed byobtaining many axial scans while scanning a sample arm beam across aspecimen, creating a two dimensional image. In order to perform LCIimaging, several strict requirements must be met by the conventionalsystems, including use of:

-   -   1. high speed reference arm delay scanning (at least 1,000        scans/second),    -   2. a high power broad bandwidth source (at least 5 mW),    -   3. a complex probe (must have at least one lens and a scanning        mechanism),    -   4. an expensive data acquisition apparatus, and    -   5. an image display.        These requirements of the conventional systems dramatically        increase the cost of OCT systems and OCT probes.

It would be desirable to have a low cost and accurate imaging system,process and needle biopsy probe having sufficient resolution that can beused by physicians with little additional training. It would also bedesirable to have a needle biopsy probe that would use conventionalsyringe and needle combinations to avoid the high cost of developing andmanufacturing custom barrels or needles. Such an exemplary system wouldalso desirably be able to provide real time, or near real time, feedbackregarding progress and location of the biopsy needle. Such a probeshould also be able to identify various tissue types and interfaces andbe able to alert a user when a target site has been reached or if aninappropriate tissue has been encountered. Interfaces are refractiveindex interfaces which occur when one tissue having optical refractiveindex is adjacent to another. The refractive index is unique to themolecular constituents of tissue and therefore interfaces occurthroughout tissue. These refractive index interfaces may give rise toscattering which is the signal detected by LCI and OCT.

Other features and advantages of the present invention will becomeapparent upon reading the following detailed description of embodimentsof the invention, when taken in conjunction with the appended claims.

SUMMARY OF THE INVENTION

The present invention generally provides devices, processes, softwarearrangements and storage media for identifying tissue types usinginterferometric ranging. The probe or disposable portion of the deviceuses a solitary single mode optical fiber, which is inexpensive and mayfit into the lumen of a clinically available needle. The solitary singlemode optical fiber can be between 125 μm and 250 μm in diameter.

According to the present invention, two dimensional imaging is notrequired. As a result, the requirements of the imaging system aresignificantly reduced. Such requirements include, but are not limited tothe use of:

-   -   1. a low power broad bandwidth source (0.001-0.5 mW),    -   2. a simple probe (does not require a lens or scanning        mechanism),    -   3. an inexpensive data acquisition apparatus,    -   4. a simple, inexpensive and small detector apparatus, and    -   5. a simplified image display or audible notification apparatus.

Accordingly, the system that uses one-dimensional interferometricranging to identify tissue according to the present invention allows fora decreased cost and size of the system console and a significantlydecreased cost of the disposable data collection probe. Disposableprobes according to the present invention may be constructed withmaterial cost far below that of existing systems, and the light sourceand detection devices required also cost significantly less than thoseof conventional OCT systems. These considerations could allow theseprobes to be used in very common procedures, such as placing anintravenous catheter or guiding a lumbar puncture. Further, due to thecost savings and reduced size of the system components, the presentinvention may be implemented in a hand-held unit.

Other features and advantages of the present invention will becomeapparent upon reading the following detailed description of embodimentsof the invention, when taken in conjunction with the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages of the invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying figures showing illustrative embodiments of theinvention, in which:

FIG. 1A is a graph of LCI reflectivity for muscle tissue.

FIG. 1B is a graph of LCI reflectivity for adipose tissue.

FIG. 2 is a schematic view of a tissue identification system accordingto one exemplary embodiment of the present invention.

FIGS. 3A-C are area schematic views of different fiber and probe designsaccording to one exemplary embodiment of the present invention.

FIG. 4 is a schematic view of an interferometric ranging probe in thelumen of a biopsy needle according to one exemplary embodiment of thepresent invention.

FIG. 5 is a schematic view of a syringe interferometric ranging probewith a single mode fiber inserted through the body of the syringeaccording to one exemplary embodiment of the present invention.

FIG. 6 is a schematic view of a syringe interferometric ranging probewith a single mode fiber inserted through the plunger of the syringeaccording to one exemplary embodiment of the present invention.

FIG. 7 is a schematic view of a syringe interferometric ranging probewith a single mode fiber inserted through an intermediate adapterbetween the syringe needle lock and the needle housing according to oneexemplary embodiment of the present invention.

FIG. 8 is a schematic view of a syringe interferometric ranging probewith a single mode fiber inserted through an adapter between the syringeneedle lock and the needle housing and includes a motion transduceraccording to one exemplary embodiment of the present invention.

FIG. 9 is a schematic view of a needle biopsy apparatus with anactivation gun according to one exemplary embodiment of the presentinvention.

FIG. 10 is a schematic view of a cannula with an interferometric rangingprobe in the body according to one exemplary embodiment of the presentinvention.

FIG. 11 is a schematic view of a cannula with an interferometric rangingprobe in the lumen according to one exemplary embodiment of the presentinvention.

FIG. 12 is a schematic view of a cannula with an interferometric rangingprobe in an electrocautery device according to one exemplary embodimentof the present invention.

FIG. 13A is a schematic view of a standard needle and housing.

FIG. 13B is a schematic view of a standard needle and a modified housingaccording to one exemplary embodiment of the present invention.

FIG. 14 is a schematic view of an interferometric ranging probe opticalconnector according to one exemplary embodiment of the presentinvention.

FIG. 15 is a schematic view of a biopsy probe with an associatedfeedback unit according to one exemplary embodiment of the presentinvention.

FIG. 16 is a schematic detail view of a gun and activation buttonaccording to one exemplary embodiment of the present invention.

FIG. 17 is a flow diagram of a method for tissue identificationaccording to one exemplary embodiment of the present invention.

FIG. 18 is a schematic view of a system configuration according to oneexemplary embodiment of the present invention.

FIG. 19 is a flow diagram of a signal processing sequence according toone exemplary embodiment of the present invention.

Throughout the figures, the same reference numerals and characters,unless otherwise stated, are used to denote like features, elements,components or portions of the illustrated embodiments. Moreover, whilethe subject invention will now be described in detail with reference tothe figures, it is done so in connection with the illustrativeembodiments. It is intended that changes and modifications can be madeto the described embodiments without departing from the true scope andspirit of the subject invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the system of the present invention, FIG. 2illustrates an tissue identification system 2 according to oneembodiment of the present invention for tissue 10 identification usinginterferometric ranging. The tissue identification system 2 utilizes aone-dimensional data set in order to identify tissue. Unlike many priorart systems, which use two-dimensional data in order to acquiresufficient information to identify tissue, the tissue identificationsystem 2 is able to identify tissue using a one-dimensional data set.Differences between two types of tissue may be understood from aone-dimensional data set. For example, FIG. 1 illustrates two graphsthat represent a one-dimensional interferometric ranging axial scan oftwo different tissue types. As can be seen from these graphs, adiposetissue (shown in the bottom graph) has a significantly different axialreflectance profile as compared to the axial reflectance profile ofmuscle tissue (shown in the top graph). The tissue identification system5 includes an imaging system 5 and a probe 50.

The imaging system 5 includes a light source 12, which is provided in aninterferometer 14. The interferometer 14 can be a fiber opticinterferometer 14. Also, while light is used in the disclosure herein asan exemplary embodiment of the light source 12, it should be understoodthat other appropriate electromagnetic radiation can be used, such as,microwave, radio frequency, x-ray, and the like. The interferometer 14or other beam splitting device known to those skilled in the art maymake use of circulators for increased sample arm power efficiency. Theinterferometer 14 includes a beam splitter 18, a reference arm 20, asample arm 24, and a communications link to at least one detector 26.The light source 12 is connected to the interferometer 14 such that thelight emitted from the light source 12 is transmitted to the beamsplitter 18. The beam splitter 18 directs portion of the light emittedby the source 12 towards a reference arm 20, while the remainder oflight is directed to a sample arm 24. The reference arm 20 includes amechanism 26. The mechanism 26 produces a time dependent optical delay.In a certain embodiment, the mechanism 26 can be a movable referencereflector or mirror. The movable reference reflector or mirror cancreate a variable time delay suitable for a specific application.

An optical fiber 29, associated with the sample arm 24, is connected toan optical coupler 58. The optical coupler 58 is also connected to anoptical fiber 25, which is inserted into the probe 50, as describedbelow. The light signals returned from the sample arm 24 and thereference arm 20 are combined by the beam splitter 18 and reflectivityas a function of depth within the tissue sample 10 (e.g., see FIGS. 1Aand 1B) is determined by measuring the interference between the two armswith at least one detector 26. Detection of a tissue birefringence(i.e., by splitting a ray into two parallel rays polarizedperpendicularly) can be accomplished by using, e.g., two detectors 26,one for each polarization eigenstate. Depending on the type ofinterferometric ranging used, one to four detectors 26 may be employed.

In a certain embodiment, one of three types of interferometric rangingcan be used: (i) optical time domain reflectrometry, (ii) spectraldomain reflectrometry or (iii) optical frequency domain reflectrometry.It should be understood that additional alternate types ofinterferometric ranging could be used with the tissue identificationsystem 2. If optical time domain reflectometry is utilized, the source12 can be is a broad bandwidth light source, the interferometer 14 isneeded, the reference arm 20 may be a low speed reference arm with delayscanning performing 20 to 50 scans per second, and the detector 26 caninclude one to four detectors. Optical time domain reflectometry isdescribed in more detail by C. Youngquist et al., “OpticalCoherence-Domain Reflectometry: A New Optical Evaluation Technique”,Opt. Lett., 12, 158-160 (1987), and K. Takada et al., “New MeasurementSystem For Fault Location in Optical Waveguide Devices Based on anInterferometric Technique”, Appl. Opt. 26, 1603-1606 (1987), the entiredisclosure of which are incorporated herein by reference. If spectraldomain reflectometry is used, the source 12 is a broad bandwidth lightsource, the interferometer 14 is required, the detection arm includes aspectrometer, the detector 26 includes a single detector, and lowcoherence interferometry data is obtained by taking the Fouriertransform of the measured spectrum. Spectral domain reflectometry isdescribed in more detail by J. Deboer et al., “Improved Signal to NoiseRatio In Spectral Domain Compared With Time Domain Optical CoherenceTomography”, Optics Letters 2003, vol. 28, p. 2067-69; and PublishedPatent No. WO 03062802, entitled “Apparatus and Method for Ranging andNoise Reduction of Low Coherence Interferometry (LCI) and OpticalCoherence Tomography (OCT) Signals by Parallel Detection of SpectralBands”, to Deboer et al., the entire disclosure of both of which areincorporated herein. If optical frequency domain reflectometry is used,the source 12 is a swept wavelength optical source, the interferometer14 is required, the detector 26 includes one to four detectors, and lowcoherence interferometry data is obtained by taking the Fouriertransform of the measured spectrum. Optical frequency domainreflectometry is described in more detail by S. Yun et al., “High SpeedOptical Frequency Domain Imaging”, Optics Express 2003, vol. 11, p.2953-63, and C. Youngquist et al., “Optical Coherence-DomainReflectometry: A New Optical Evaluation Technique, Opt. Lett., 12,158-160 (1987), and K. Takada et al., “New Measurement System For FaultLocation In Optical Waveguide Devices Based on an InterferometricTechnique”, Appl. Opt. 26, 1603-1606 (1987), the entire disclosure ofboth of which are incorporated herein.

In an alternate embodiment of the present invention, the interferometer14 is a Mach-Zehinder interferometer, a Michelson interferometer, anon-reciprocal or circular interferometer, a Sagnac interferometer, aTwyman-Green interferometer and the like. In another alternateembodiment of the present invention, the interferometer 14 is aninterferometer as described in U.S. Provisional Application Ser. No.60/514,769 filed Oct. 27, 2003, entitled “Apparatus and Method fromPerforming Optical Imaging Using Frequency-Domain Interferometry,” thedisclosure of which is incorporated herein by reference in its entirety.

A probe 50 can include a biopsy device 51, which includes a needle 52having a bore (not shown) associated with a syringe 54 through which theoptical fiber 25 is introduced. The fiber 25 may be inserted into theprobe 50 and in turn into the needle 52. The needle 52 and fiber 25 canbe inserted percutaneously (or otherwise) toward the tissue 10 to besampled. In other exemplary embodiments, the needle 52 can be a genericbarrel, a specialized barrel, a needle, a stylet, and the like.

Referring now to FIG. 3, the fiber 25 includes a cladding 60 and acleaved anoptical fiber core 62, as shown in portion A of FIG. 3. Whenlight signal is directed through the fiber 25 it forms a beam waist 64.The beam waist may be about 9 μm in diameter. Other lenses or opticalelements may be attached to the fiber 25 to allow for focusing deeperinto tissue, including a gradient index lens 66 (see portion B of FIG.3), sometimes referred to as a GRIN lens, a ball lens 68 (see portion Cof FIG. 3), a drum lens, a microlens, a tapered fiber end, a prism andthe like. Alternatively, the fiber 25 may be angle cleaved or otherwiseconfigured to produce an arbitrary pattern of electromagnetic radiation.In a certain embodiment, the cladding 60 has an outer diameter of 125 μmand the anoptical fiber core has an outer diameter of 9 μm.

For needle biopsies that are traditionally performed using computerizedtomography (CT), magnetic resonance imaging (MRI), or ultrasoundguidance, the fiber 25 may be inserted into the biopsy needle 52 asshown in FIG. 4 and may be embedded within the needle biopsy device, orinserted through the lumen 70 of the needle 52. These types ofprocedures do not use fine needle aspiration. The lump or mass is notmanually identifiable, but can only be identified through some othernon-invasive imaging technique, such as CT or MRI. These and otherguided needle biopsy procedures may use a larger and longer needle,while still utilizing the fiber 25 to assist in guiding the biopsyprocedure.

To insert the fiber 25 into the needle 52 of the probe 50 for fineneedle aspiration, the fiber 25 may be inserted through an aperture 72,wherein FIG. 5 does not shown the aperture 72 in the body, in the bodyof the syringe 51 and then (i) into the needle 52 as shown in FIG. 5,(ii) through the plunger 74 of the syringe 51, and then provided intothe needle 52 as shown in FIG. 6, (iii) through an intermediate piece 76that is attached between the syringe 51 and the needle 52 as shown inFIG. 7, and/or by other insertion configurations. The probe 50 can beconfigured to allow suction for the aspiration of cells from the tissue10, while allowing free movement of the fiber 25 at the tip of theneedle 52.

In an exemplary embodiment, as shown in FIG. 8, the use of anintermediate coupler or holder between the syringe and the needle can beutilized. This would allow the use of standard needles and syringes. Inthis exemplary embodiment, a probe 100 utilizes the imaging system 5 asdescribed above to identify tissue. The probe 100 includes an inputfiber 102 attached to the imaging system 5 at one end, and to an opticalconnector 58 at the other end. The optical fiber 102 is connected to asingle mode input fiber 104. The optical fiber 102 is inserted throughan intermediate adapter 106, located between a syringe 108 and a needlelock 110. A needle 112 is attached to the needle lock 110. A motiontransducer 114 may be used as a result of too little space between theouter surface of the fiber 104 and the inner bore surface of the needle112. The motion transducer 114 generally allows the fiber 104 to berepositioned in order to allow aspiration of the tissue 10. The motiontransducer 114 can be a manual motion transducer, an automated motiontransducer, or the like. In another exemplary embodiment of the presentinvention, the needle lock 110 is a Luer lock.

FIG. 9 illustrates a tissue identification system 122 that includes thesyringe 108 held within a device known in the art as a gun 120. Thisconfiguration allows for easy aspiration of the tissue 10 into the boreof the needle 112. Many of the components described above can also beincorporated into the tissue identification system 122 for easy accessand convenience.

FIG. 10 illustrates an exemplary operation of placing a cannula 200 forIV access, pleural, perioneal taps, and the like according to a furtherembodiment of the present invention. The cannula 200 includes a guidecatheter 202 and a fiber optic probe 204. The fiber optic probe 204 isprovided within the guide catheter 202. Alternatively, the probe 204 maybe inserted through the lumen 206 of the guide catheter 202 as shown inFIG. 11.

FIG. 12 illustrates an intra-operative exemplary embodiment 300 of aprobe 306 according to still another embodiment of the presentinvention. The probe 306 is incorporated into an electrocautery device301. An optical window 302 may be placed near the distal fiber tip 304to protect the probe 306 against thermal damage by the cautery electrode308. In yet another embodiment, the probe 306 may be incorporated into ascalpel, an independent hand-held device and the like instead of beingincorporated into the electrocautery device 301. The optical window 302can be made of sapphire.

In order to allow for easy insertion of the fiber optic probe 25 intothe needle 52, the internal lumen 400 of a standard needle housing 402,as shown in section A of FIG. 13, can be modified such that the internallumen 404 of a modified needle 406 is tapered, as shown in FIG. 13B.

FIG. 14 illustrates an interferometric ranging probe optical connector500, which is one side of the optical coupling 58, which can be usedaccording to the present invention. The optical coupling 58, whichconnects the probe 50 to the imaging system 5, should be robust andsimple to use. In another embodiment, the optical coupling 58 includes abare fiber connector attached to the probe 50, which is relativelyinexpensive, and the interferometric ranging probe optical connector 500attached to the imaging system 5, which is relatively expensive. The useof a bare fiber connector attached to the probe 50 does not increase thecost of the probe 50. The more expensive portion of the optical coupling58 is attached to the imaging system 5. The interferometric rangingprobe optical connector 500 is constructed so as to engage with a barefiber connector, such that a robust connection is made. Theinterferometric ranging probe optical connector 500 may include acleaved (angle cleaved) fiber 502 (the proximate end of which isconnected to the imaging system 5, not shown for the sake of clarity)inserted through a housing 504 having a ferrule 506 connected to atapered v-groove 508. The tapered v-groove 508 is terminated by a fiberstop 510. The housing 504 has a taper 516 at one end through which afiber 518 is inserted. The fiber 518 is inserted into the housing 504via the taper 516 until it reaches the fiber stop 510. Once the fiber518 comes to a stop, a clamp 512 holds the fiber 518 in place, away fromthe fiber-fiber interface, such that an air or fluid gap 514 ismaintained. The fiber 518 is connected to the probe 50. In anotherembodiment, coupling gel may be used with flat cleaves to eliminateback-reflection from the gap 514.

A number of optional mechanisms or apparatus configured to communicatespecific information to a user regarding the tissue 10 being encounteredby the tissue identification system 2 during a procedure may be used.FIG. 15 illustrates a schematic diagram of a system 600 with componentsof an imaging system 5 and the optical fiber 29 connected to the fiber25 via the optical connector 58. The fiber 25 is operatively associatedwith a syringe 51 and passes through the bore of a needle 52. A holder612 is associated with the syringe 51 by the syringe barrel 614. Afeedback unit 620 can be associated with the holder 612 in any ofseveral ways.

The holder 612 can be attached to the syringe 51. In an exemplaryembodiment, the holder 612 is removably attachable to the syringe 51,such as, but not limited to, snap fit, removable adhesive, clamping,clipping or the like. By having the holder 612 be removably attachableto the syringe 51, the holder 612 and associated feedback unit 620 canbe reused while the syringe 608 can be disposable, thereby enablingconventional syringes to be used and eliminating the need for a customdeveloped and expensive probes.

In another embodiment, the holder 612 is removably attachable to thesyringe 51 using a gun or syringe holder. In another certain embodiment,the system 600 is integrally related to the gun (described above inrelation to FIG. 9). In still another embodiment, the system 600 isembedded within the gun 634, which holds the feedback unit 620 and fiber606 and improves the ability of the physician to aspirate tissue intothe needle 610.

The feedback unit 620 provides information to the user of the system600, including that the system 600 has detected tissue of a particulartype. In another embodiment, the feedback unit 620 is a visual display,such as, LED, VGA, or other visual feedback system. With an LED display,the software algorithm and tissue identification determinations, asdescribed hereinbelow, can use an output signal to drive one or moreLEDs, which can be actuated when the probe tip passes through or inproximity to differing tissue interface types (e.g., adipose versusmuscle). As the tip contacts tissue of interest, such as a masticularlump, an LED light can change color or a different colored LED can beactuated to provide the physician feedback that the lump has beencontacted and that the biopsy aspiration or other sampling can commence.

In still another embodiment of the present invention, the feedback unit620 is an audible tone generator, which provides audio feedback asdifferent tissue or other structures are detected by the system 600. Ina further embodiment, the feedback unit 620 is a vibration generator.Each of the visual, audio and vibration feedback units provide simpleand yet useful feedback to users of the system 600 to better target abiopsy probe in real time and with confidence. In yet anotherembodiment, the feedback unit 620 is a visual display screen that can beused to display a one or two-dimensional rolling plot image, comprisingaccumulated backscattered intensity as a function of z or depth withintissue, i.e. I_(z), over time to form an image. The visual display canbe a conventional CRT display or an LCD display for providing moredetailed or multimodal feedback. The visual display can be as small asor smaller than a conventional cell phone display or large to afford theuser of the system 600 with a magnified view of the tissue 10.

The feedback unit 620 is communicatively coupled to the imaging system602 by a physical cable connection 622 or via a wireless connection. Thewireless connection can be a radio frequency (“RF”) connection,electromagnetic radiation signal, or the like. A wireless signalconnection allows for reduced weight of the biopsy probe and fewer wiresin the surgical site. A simple feedback system can be utilized so thatthe physician can operate the biopsy probe with one hand and havefeedback proximate to the probe body so that the physician'sconcentration and visual focus does not leave the biopsy area.

FIG. 16 illustrates a further embodiment of the feedback unit 620including a display 630, a manually operated button or switch 632 and agun 634. The switch 632 is operatively connected to the display 630. Theactuation of the switch 632 causes the display 630 to show selection ofstandard biopsy procedures, such as, but not limited to, biopsy ofbreast tissue, liver tissue, spleen tissue, muscle tissue, lymph tissue,kidney tissue, prostate tissue and the like. Each of these biopsyprocedures involves the probe 50 passing through relatively consistenttypes of layers, including skin, muscle, fascia, and the like, in asimilar order for a given procedure. For example, for a lumbar puncture,the order of layers the probe 50 would encounter are skin fascia,vertebrae, muscle, fascia, disk, subdural space, epidural space, thespinal cord fluid area. Each of these tissues can produce a relativelyconsistent and determinable imaging signal peak which, when normalizedover a substantial patient base by comparative image analysis andsubtracting the curves of normalized data versus actual patient data,offers an accurate picture of what will be encountered during the biopsyprocedure.

As the needle tip passes through each layer, the imaging system 600detects the actual signal, and compares it to reference signals storedin a database. By taking an interferometric ranging scan of, forexample, z (shown in FIG. 1) to obtain I(z), and taking the derivativedI/dz over time, a series of lines corresponding to the peaks of thesample may be obtained. The various consecutive peaks can be displayedby the feedback unit 620 to provide the user with accurate feedback ofwhere the probe is and to assist the user in guiding the probe to thetarget area. The feedback unit can also incorporate an “anti-algorithm”to provide immediate feedback if the probe has wandered, overshot thetarget site or encountered a tissue type not expected to be detectedduring a particular procedure, such as, in the example of lumbarpuncture, if the probe has passed the target area and hit a nerve. Suchfeedback can enable the physician to relocate the probe tip to theappropriate area.

The system and process according to the present invention is also ableto determine when a target site has been reached. In order to determinewhen a target site has been reached, the system processes data from thereflected light to look for backscattering signatures that areindicative of a tissue type within the target site during a givenprocedure. Such processing consists of feature extraction and insertingthese features into a model that predicts tissue type. This model can bea physical model, a chemometric model, or a combination of the two. Aphysical model generally predicts the scattering signal based onphysical principles of light scattering. A chemometric model uses atraining set and statistically extracts features using techniques suchas Partial Least Squares (“PLS”) or Principle Component Analysis(“PCA”). Such model is developed based on known samples, and the newdata can be tested using this model. It should also be understood thatfringes may be acquired and processed to determine other tissue featuresincluding birefringence, Doppler flow, and spectral characteristics.

Tissue identification can be accomplished by visualizing the intensity,birefringence, Doppler, spectroscopic axial reflectivity profile and/orthe like. Additionally, the frequency spectrum (Fourier transform of theintensity data) of the reflectivity scan will provide informationrelating to the spacing of the scattering structures in the tissue whichrelates to tissue structure. A more sophisticated analysis, including,but not limited to, variance analysis, one-dimensional texturediscrimination (including fractal dimension, spatial gray levelco-occurrence matrix parameters, Markovian distance, edge counting),power spectral analysis (including Fourier domain and time domain),n^(th) order histogram moment analysis, and temporal analysis of thereflectivity information (comparing one scan to another separated by afixed time) using correlation techniques will provide informationrelating to the type of tissue observed. Other key quantitative metricsthat may be used to characterize tissue types include, measurement ofthe backscattering coefficient, total attenuation coefficient,estimation of the anisotropy coefficient (particle size) from the onsetof multiple scattering, particle shape and size from the detectedspectrum using coherence-gated light scattering spectroscopy, and thelike.

The following illustrative list of tissue characteristics may be foundusing the system and process of the present invention: adipose tissue,muscle tissue, collagen, nerve tissue, lymph node tissue, necrosistissue, blood, glandular tissue and the like. Adipose tissue exhibitslow absorbance at water peaks, high low spatial frequency componentsfrom the LCI intensity image and a high anisotropy coefficient. Muscletissue exhibits high absorbance at water peaks, moderate birefringence,moderate anisotropy and decreased variance. Collagen exhibits very highbirefringence. Nerve tissue exhibits moderate to high birefringence,high water absorbance and decreased power spectral density. Lymph nodetissue exhibits a low anisotropy coefficient and a low temporalvariance. Necrotic tissue exhibits high temporal variance of LCI signal,high attenuation coefficient, high water absorbance and lowbirefringence. Blood exhibits high Doppler shift, high water absorbance,high total attenuation coefficient, and high temporal variance.Glandular tissue exhibits moderate spatial frequency variance and lowbirefringence. It should be understood that the present inventioncontemplates the use of more than one analysis method, i.e., amultimodal system. This may provide enhanced detection and analysis oftissue types.

FIG. 17 illustrates a process 700 for differentiating fat tissue fromfibrous tissue according to an exemplary embodiment of the presentinvention. The signal measured by the system 600 is an average of anumber M axial scans. The system 600 detects the tissue sample surfaceusing a signal threshold T1 at block 702. The detected signal is dividedinto N number of windows at block 704. Signal processing is conducted atblock 706 to obtain a parameter derived from the interferometric rangingsignal, such as the average deviation (ADEV) or standard deviation(STDEV) of the signal in each window (such as, but not limited to, thetechnique described in “Numerical Recipes in C”, Press, W. et al.,Cambridge University Press, New York, N.Y. 1992, the entire disclosureof which is incorporated herein by reference) is calculated. Each windowtested to determine if the threshold T2 is exceeded to obtain the tissuetype as a function of depth z at block 708. If, at block 710, the system600 determines that ADEV (or STDEV) is greater than the threshold T2,the tissue is considered to be lipid, and the process 700 advances toblock 712. Otherwise, the tissue is not likely to be lipid and theprocess 700 advances to block 714.

Applications of this technology can include tissue identification forthe purpose of intraoperative guidance, needle biopsy guidance, fineneedle aspiration, image guided biopsy, guiding placement of peripheralor central intravenous or intra-arterial catheters, and the like.Different methods of imaging can be used for different applications.These different applications include: guided biopsy; cell methodology;veni-arterio, pattern or Doppler recognition; lumbar, pattern; therapyguidance, pattern and optical methods; and the like. The probe 50 canalso be used as a targeting and delivery device for therapeutics. Theprobe 50 can image the target area to make sure that needle injection ofa therapeutic has reached and/or entered the target tissue or site bydetecting the tissue type and interface change, i.e. a change in therefractive index of the tissue.

In order to determine whether the tissue is fibrous tissue or fattissue, the process 700 utilizes standard image processing techniques toprocess data in order to differentiate fibrous (adipose) and fat tissue.Table 1, below, illustrates different measurements of fibrous andadipose tissue following the image processing of the data: TISSUE TYPESENS SPECIFICITY Fibrous .95 .98 Adipose .97 .94 Fibrous/Adipose .96 .84In the table above, sensitivity is true positive, i.e. truepositive+false negative, while specificity is true negative, i.e. truenegative+false positive.

FIG. 18 illustrates an interferometric ranging diagnostic system 800 foridentifying tissue according to the present invention. The system 800uses a light source configured to emit light having a optical wavelengthof 1.3 microns, 300 microwatts power and a 48 nm bandwidth. The lightsource allows the system 800 to interrogate tissue with a 15 micronresolution. The system 800 utilizes a low scanning frequency of thereference arm because building a coherent image is not the purpose ofthe system 800. Information can be gathered to identify the tissuethrough an average of several A-scans. The A-scan can be performed byone sweep of the reference arm, which corresponds to one depth scan. Thesystem 800 processes and stores digital data, and the tissue typeinformation is displayed on the feedback device in real time.

The LED source of the system 800 is a 300 microwatts SUPERLUM LED, whichcan be temperature and current controlled. The light is linearlypolarized using a fiber optic polarizer P and sent to a beam splitter.The sample is interrogated with two orthogonally polarized states of thelight in order to get birefringence information. The two orthogonallypolarized states of the light are created by passing the light throughthe beam splitter, to two polarization controller PC paddles, one ineach arm of the beam splitter. The two orthogonal polarization statesare sent alternatively to the fiber optic circulator CIR, which directsthe light to the fiber optic Michelson interferometer IF. The opticalswitch OSW is synchronized with the optical delay line ODL galvanometer,so that the polarization would change alternatively from one scan to theother. A very simple delay line, consisting in a retroreflector mountedto an lever driven by a galvanometer, was used to do the depth scanning.The probe attached to the sample arm of the interferometer IF includes abare fiber introduced into a syringe needle. The backscattered light iscoherently added to the light coming from the ODL and sent to thedetectors D1, D2. A polarization splitter PS is used to select the twoorthogonal states. The output signals of the detectors are preamplifiedand digitized using a NI DAQ card.

The system performs the digital acquisition, filtering, and averaging ofthe fringes, and provides the following information: (1) depth intensityat 15 microns resolution and spectral information, (2) birefringenceinformation: computes stokes parameters-IQUV and extracts phaseretardation, and (3) Doppler shift information.

FIG. 19 illustrates a flow diagram 900 of the signal processing sequenceaccording to an exemplary embodiment of the present invention. Thesimplest form of tissue identification is differentiation of two tissuetypes. The difference between two tissue types can be seen in FIG. 1,which shows the results of a feasibility study to distinguish cadaverfat from fibrous tissue. For example, adipose tissue has an appearanceof multiple peaks separated by low interferometric ranging signalsegments, whereas fibrous tissue has a lower degree of variance anddecays exponentially.

Although only a few exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention as defined inthe following claims. It should further be noted that any patents,applications or publications referred to herein are incorporated byreference in their entirety.

1. An apparatus for identifying characteristics of tissue, comprising: aradiation source configured to perform an axial scan of the tissue usingradiation; and an imaging system adapted to receive axial scan radiationbased on the axial scan, and to process data relating to the axial scanradiation to identify characteristics of the tissue.
 2. The apparatus ofclaim 1, wherein the radiation source is a light source configured toemit light.
 3. The apparatus of claim 2, wherein the light source is abroad bandwidth light source.
 4. The apparatus of claim 2, wherein thelight source is a swept wavelength optical source.
 5. The apparatus ofclaim 2, wherein the light source delivers radiation to the tissue viaan optical fiber disposed in an insertion device having a distal end atleast partially disposed within the insertion device and a proximal end.6. The apparatus of claim 5, wherein the insertion device is configuredto provide the distal end of the optical fiber adjacent to the tissue.7. The apparatus of claim 5, wherein the insertion device is one of abarrel, a needle, and a stylet.
 8. The apparatus of claim 1, wherein theimaging system further includes an interferometer adapted to direct aportion of the radiation emitted by the radiation source into a samplearm and detecting radiation reflected from the tissue back through thesample arm.
 9. The apparatus of claim 8, wherein the interferometerdirects another portion of the radiation into a reference arm.
 10. Theapparatus of claim 9, wherein the imaging system identifiescharacteristics of the tissue by processing the axial scan radiation toprovide the characteristics of the tissue, the axial scan radiationincluding radiation received from the reference arm and radiationreceived from the sample arm, and comparing the characteristics of thetissue with a database of normalized characteristics of a plurality oftissue types.
 11. The apparatus of claim 10, wherein the axial scanradiation includes at least one of backscattering, spectral properties,birefringence and Doppler shift.
 12. The apparatus of claim 10, whereinthe imaging system processes the axial scan radiation by performing atleast one of standard deviation, average deviation, and slope of theaxial reflectivity profile.
 13. The apparatus of claim 10, wherein theimaging system inputs data derived from the axial scan radiation into astatistical model to predict tissue type.
 14. The apparatus of claim 13,wherein the statistical model extracts features from data derived fromthe axial scan radiation.
 15. The apparatus of claim 13, wherein thestatistical model is at least one of partial least squares or principlecomponent analysis.
 16. The apparatus of claim 1, wherein the imagingsystem identifies the characteristics of the tissue by determiningreflectance characteristics of the axial scan radiation usinginterferometric ranging, and comparing the characteristics of the tissuewith normalized reflectance characteristics of a plurality of types oftissue stored in a database.
 17. The apparatus of claim 16, wherein thetype of interferometric ranging is at least one of optical time domainreflectometry, spectral domain reflectometry and optical frequencydomain reflectometry.
 18. A method for identifying characteristics oftissue, comprising the steps: performing an axial scan of the tissueusing radiation; and processing data relating to the axial scanradiation based on the axial scan to identify characteristics of thetissue.
 19. The method of claim 18, wherein the axial scan radiationincludes at least one of backscattering, spectral properties,birefringence and Doppler shift.
 20. The method of claim 18, wherein theprocessing step identifies the characteristics of the tissue byperforming at least one of standard deviation of data associated withthe axial scan radiation, average deviation of data associated with theaxial scan radiation, and slope of the axial reflectivity profile ofdata associated with the axial scan radiation.
 21. The method of claim18, wherein a light source delivers the radiation to perform the axialscan of the tissue via an optical fiber disposed in an insertion devicehaving a distal end at least partially disposed within the insertiondevice and a proximal end.
 22. The method of claim 18, wherein theprocessing step identifies the characteristics of the tissue byinputting data derived from the axial scan radiation into a statisticalmodel to predict tissue type.
 23. The method of claim 18, wherein theprocessing step identifies the characteristics of the tissue bydetermining reflectance characteristics of the axial scan radiationusing interferometric ranging and comparing the characteristics of thetissue with a database of stored normalized reflectance characteristicsof a plurality of types of tissue.
 24. A storage medium storing asoftware program for identifying characteristics of tissue, wherein thesoftware program, when executed by a processing arrangement, isconfigured to cause the processing arrangement to execute the stepscomprising of: performing an axial scan of the tissue using radiation;and processing data relating to the axial scan radiation to identifycharacteristics of the tissue.
 25. The storage medium of claim 24,wherein the axial scan radiation includes at least one ofbackscattering, spectral properties, birefringence and Doppler shift.26. The storage medium of claim 24, wherein the processing stepidentifies the characteristics of the tissue by performing at least oneof standard deviation of data associated with the axial scan radiation,average deviation of data associated with the axial scan radiation, andslope of the axial reflectivity profile of data associated with theaxial scan radiation.
 27. The storage medium of claim 24, wherein alight source delivers the radiation to perform the axial scan of thetissue via an optical fiber disposed in an insertion device having adistal end at least partially disposed within the insertion device and aproximal end.
 28. The storage medium of claim 24, wherein the processingstep identifies the characteristics of the tissue by inputting dataderived from the axial scan radiation into a statistical model topredict tissue type.
 29. The storage medium of claim 24, wherein theprocessing step identifies the characteristics of the tissue bydetermining reflectance characteristics of the axial scan radiationusing interferometric ranging and comparing the characteristics of thetissue with a database of stored normalized reflectance characteristicsof a plurality of types of tissue.
 30. A logic arrangement foridentifying characteristics of tissue, which, when executed by aprocessing arrangement, is operable to perform the steps comprising of:performing an axial scan of the tissue using radiation; and processingdata relating to the axial scan radiation to identify characteristics ofthe tissue.
 31. The logic arrangement of claim 24, wherein the axialscan radiation includes at least one of backscattering, spectralproperties, birefringence and Doppler shift.
 32. The logic arrangementof claim 24, wherein the processing step identifies the characteristicsof the tissue by performing at least one of standard deviation of dataassociated with the axial scan radiation, average deviation of dataassociated with the axial scan radiation, and slope of the axialreflectivity profile of data associated with the axial scan radiation.33. The logic arrangement of claim 24, wherein a light source deliversthe radiation to perform the axial scan of the tissue via an opticalfiber disposed in an insertion device having a distal end at leastpartially disposed within the insertion device and a proximal end. 34.The logic arrangement of claim 24, wherein the processing stepidentifies the characteristics of the tissue by inputting data derivedfrom the axial scan radiation into a statistical model to predict tissuetype.
 35. The logic arrangement of claim 24, wherein the processing stepidentifies the characteristics of the tissue by determining reflectancecharacteristics of the axial scan radiation using interferometricranging and comparing the characteristics of the tissue with a databaseof stored normalized reflectance characteristics of a plurality of typesof tissue.
 36. An apparatus for identifying characteristics of tissue,comprising: a radiation source configured to deliver radiation to thetissue; and an imaging system adapted to receive the radiation andprocess unidimensional data relating to the radiation to identifycharacteristics of the tissue.
 37. An apparatus for identifyingcharacteristics of tissue, comprising: at least one optical fiber, oneof the at lest one optical fiber disposed in a needle having a distalend at least partially disposed within the needle and a proximal end,the distal end of the one of the at least one optical fiber adapted tobe placed adjacent to tissue; and, an imaging system in communicationwith the proximal end of the one of the at least one optical fiber, andconfigured to process reflected light from the at least one opticalfiber to identify the tissue.
 38. The apparatus of claim 37, wherein thereflected light is unidimensional light.
 39. The apparatus of claim 37,wherein the reflected light is generated to perform an axial scan.